Erosion refers to the wear-and-tear process that wears away at rocks, soil and other geological materials; while deposition refers to their deposition in another location.
Streams–from rivulets to rivers–complete the hydrologic cycle by transporting weathered materials back into the oceans through erosion and deposition processes, both physical and chemical in nature.
Water
Water erosion refers to the process of dislodging sediment from the ground by means of flowing water, most often rain or snowmelt. This causes activities such as gully and rill erosion, streambank slumping and floodplain sand accumulation that can have downstream consequences including flooding, sedimentation and decreased soil fertility.
Rainfall plays a critical role in determining how much sediment leaves a site, but other influential elements include slope, ground texture (clay, silt and sand), slope angle and the nature of any underlying rocks that could influence this loss of material.
Land that lacks vegetation–for instance, fields plowed before or after growing crops and pastures subjected to heavy livestock grazing–is particularly susceptible to erosion from water sources, as climate conditions such as drought and drastic temperature shifts make soil even more vulnerable. Erosion transports nutrients bound up in its particles into both terrestrial and aquatic ecosystems, potentially disrupting them and having adverse consequences for both.
Wind
Wind erosion is the result of wind-driven transport and deposition of soil particles by wind currents, and causes severe environmental degradation by discharging fine nutrient-rich surface soil particles into water bodies, air spaces, or other locations, thus decreasing cropland productivity while increasing human-related hazards.
Entrainment is an integral component of erosion; it involves pulling particles into the moving medium using forces such as fluid drag, horizontal lift and vertical lift. Entrapment relies on forces strong enough to overcome cohesive bond resistance as well as frictional resistance due to surface characteristics on particles.
Wind and wave erosion create various natural landforms, from beaches and river deltas to sediment deposits which supply vital nutrients for agricultural development, while simultaneously altering the landscape by providing shelter to plants and animals. Wind erosion plays an integral part in spreading seeds and spores – essential processes in plant survival.
Ice
At a continental ice sheet scale, a hierarchy of environmental and internal controls determine erosion patterns. These include climate, lithology, topographic relief and the dynamically evolving thermomechanical ice-sheet configuration12.
An age-elevation relationship derived from bedrock thermochronology was used to derive an age-thermomechanical ice sheet model and estimate glacial erosion within northwest Eurasia (Supplementary Table 1). Erosion rates generated from this simulation closely align with empirical long-term denudation data across Fennoscandia as well as showing clear zonation along geological provinces due to fluctuating ice fluxes (Supplementary Table 1).
However, detrital thermochronological ages aren’t as easy to interpret as suggested by the hypsometric data due to local variations in erosion rates: for instance, detritus produced on hillslopes tends to contain higher proportions of older age peak components as shown by their SPDFs in Fig 9. Frontal moraine sediments also tend to exhibit a lower age peak component than hillslope sources due to storage by tributary glaciers that transport it downstream.
Human Activity
Erosion involves weathering, which involves the breakdown and dissolution of rocks and minerals, followed by deposition, which involves depositing sediment at various places throughout a landscape. Human activity has an impactful influence on both processes.
Sediments can be distributed by wind, water, ice or gravity; erosion can also cause sudden landform collapses such as mountains or other landforms collapsing into each other.
Human activities play a large part in soil erosion. Farming and construction activities both play their parts. Plants and trees help hold down soil; when people cut them down for food or housing purposes, however, leaving unprotected and vulnerable to wind and rain erosion.
Overgrazing is another key human influence. Animals consume too much protective vegetation or compact the soil when grazing, which increases erosion risks in areas that are flat and dry. Erosion may also accelerate when people dig into the Earth to remove surface layers – another significant human influence.